Production of aldol



Patented Apr. 25, 1933 UNITED STATES GEORGE FREDERICK HORSLEY, or noR'ron-on-rnns, GLANDI Assiemamo'm PERIAL CHEMICAL INDUSTRIES LIMITED, or. LONDON, ENGLAND, A BRIr sn; COM- PANY No Drawing. Application filed January 29, 1929, Serial No. 386,016,'andii1 Great Britain February PRODUCTION or annoi.

This invention relates to the production of aldol and crotonaldehyde starting from acetaldehyde. It is known to condense acetaldehyde in the presence of alkali both at low and at raised temperatures, e. g. 30 40 0. Various sources of alkali have been proposed, and in various concentrations. Thus it has been proposed to effect the condensation of acetaldehyde to aldol by means of potassium carbonate solution used in a concentration equal to a 0.4 normal solution: it has also been proposed to use 0.1 normal caustic soda solution. A saturated solution of baryta has also been recommended. It has also been proposed to use a limited quantity of dilute aqueous solution of caustic alkali so that the amount of caustic alkali present in the reaction mixture is not more than about 0.02 per cent. of the quantity of acetaldehyde.

It is also known to carry out the reaction in the medium formed by aldol and acetaldehyde, and to perform the condensation and distillation of the products while excluding oxygen.

According to the present invention the condensation of acetaldehyde to aldol is carried out while excluding oxygen in neutral or very faintly alkaline solution such that the concentration of hydroxyl ions is not greater than one hundred-thousandth normal. The smallest degree of alkalinity that has hitherto been suggested, namely an amount of alkali equal to 0.02 per cent of the acetaldehyde, is several hundred times the maximum permitted according to this invention. According to another feature of the invention the solution is buffered for example by addition of a metal acetate such as sodium acetate which may or may not act as a condensing agent preferably in conjunction with an amount of acetic acid sufficient to depress the concentration of hydroxyl ions to the neutral point or to within the limits already indicated.

The presence of acetate ions in the solution minimizes the effect of an accidental increase in the acetic acid concentration that might be occasioned by oxidation of the acetaldehyde if oxygen should find its way into the solution. The 'reaction is preferably carried out at moderately raised temperatures, e.- g. 30 C. t V V Ewample I Il'lfl/ continuous small scaleplant, 52 kilo-' grammes of liquid acetaldehyde were intro duced daily into a reaction vessel containing a reaction medium composed of 40 parts ofaldol,40 parts of acetaldehyde and 20 parts of water, and containing '3 grammes per litre of sodium acetate and a trace ofacetic acid corresponding to a concentration of- 0.'0001 normal. Thefconten-ts of the reaction vessel were maintained at a temperature of 30 by means of cooling coils, andastream of inertgas was continuously passed over thei 'surface of the reaction liquor; 13 kilo grammes per day of'a 1 per cent. aqueous solution of sodium acetatewereadded to the reaction liquor, and'from time to time a test was taken on-the liquor- If it was no longer neutral (pH= 7') either-acid or alkali was added-to adjust the balance.

The-"necessary amount of reaction liquorwas continuously withdrawn to keep a'constant quantity present in the vessel, andthis withdrawn liquor was acidified by the addition of 0.4 kilogrammes per day of 20 per cent. sulphuric acid. The liquor was then distilled, the acetaldehyde vapors given ofl being returned to the reaction vessel, and the aldol being converted into crotonaldehyde' and water. The crotonaldehyde. distilled off in the form of a binary azeotropic vapor with water, containing 74 per cent. of crotonaldehyde and 26 per cent of water.

This vapor on condensation separated into two layers, the upper one being rich in crotonaldehyde and the lower one rich in water. By distilling the liquid forming the upper layer a further quantity of binary vapor was evolved, which was condensed and added to the previous condensate, and pure crotonaldehyde was obtained from the residue. The aqueous layer on distillation yielded a quantity of binary vapor and a residue of water which was rejected.

I declare that what I claim is 1. Process of producing aldol which consists in condensing acetaldehyde in neutral solution, While excluding oxygen.

2. A process of producing aldol which consists in condensing acetaldehyde in a buffered neutral solution. 1 1

3. Process of producing 'aldol'which con.- sists in condensing acetaldehyde in presence of an alkali metal acetate.

4;. Process of producing aldol which-consists in condensing aceta'ldehyde in presence of an acetate and suflicient acetic acid p I to neutralize the hydroxyl ions formed by hydrolysis of the said acetate.

5. Process of producing aldol Which consists in condensing acetaldehyde in absence" of oxygen and in presence of an acetate and sufiicient acetic acid to neutralize the hydroxyl ions formed by hydrolysis \of the said p I acetate.

6. In the process .ofproducing aldol, the step which comprises condensing acetaldehyde inthe presence of asolution having a hydroxyl ion concentration of from 10- to 10-, normal. I

V 7,. In the process of producing aldol, the ste which comprises condensing acetaldeby e in the presence of a solution having a hydroxyl ion concentration oi from 10 to 10 normal in the presence of a buffer salt. a

8. In the process of producing aldol, the step which comprises condensing acetaldehyde in the presence of a solution having a hydroxyl ion. concentration of from 10- to 10* normal in the presence ofa buffer salt, and an amount of acetic acid sufficient to maintain the concentration of hydroxylions Within the limitsindicated. In Witness whereof, I haye hereunto signed my name this 11th day of January, 1929. GEORGE FREDERICK HORSLEY. 

